Photothermographic composition, element and process

ABSTRACT

Improved sensitivity to certain wavelengths of light and improved contrast are provided by certain photothermographic compositions containing a sensitizing concentration of a nonsilver iodide salt. Such photothermographic compositions, prepared by (A) preparing a dispersion of (a) an oxidationreduction image-forming combination comprising (i) a silver salt oxidizing agent and (ii) an organic reducing agent, with (b) ex situ, synthetic polymer-peptized photosensitive silver halide, (c) a cyclic imide toner in (d) a non-gelatin polymeric binder, contain a sensitizing concentration of a non-silver iodide salt, such as lithium iodide. The described non-silver iodide salt can be mixed with described photothermographic compositions at different stages of preparation of the compositions.

United States Patent Jones PHOTOTI-IERMOGRAPHIC COMPOSITION, ELEMENT AND PROCESS Cynthia G. Jones, Leroy, N.Y.

Eastman Kodak Company, Rochester, NY.

Filed: Jan. 2, 1974 Appl. No.: 430,364

Inventor:

Assignee:

US. Cl 96/67, 96/94 R, 96/108, 96/114, 96/114.1, 96/114.6

Int. Cl G03c l/28 Field of Search 96/114.1, 67, 94 R, 108, 96/114.6, 114

References Cited UNITED STATES PATENTS 4/1965 Fix 9/1970 3/1972 Burt et a1 96/64 Primary Examiner-Norman G. Torchin Assistant Examiner-Alfonso T. Suro Pico Attorney, Agent, or FirmR. E. Knapp [57] ABSTRACT Improved sensitivity to certain wavelengths of light and improved contrast are provided by certain photothermographic compositions containing a sensitizing concentration of a non-silver iodide salt. Such photothermographic compositions, prepared by (A) preparingia dispersion of (a) an oxidation-reduction imageforming combination comprising (i) a silver salt oxidizing agent and (ii) an organic reducing agent, with (b) ex situ, synthetic polymer-peptized photosensitive silver halide, (c) a cyclic imide toner in (d) a nongelatin polymeric'binder, contain a sensitizing concentration of a non-silver iodide salt, such as lithium iodide. The described non-silver iodide salt can be mixed with described photothermographic compositions at different stages of preparation of the compositions.

20 Claims, N0 Drawings 1 PHOTOTIIERMOGRAPHIC COMPOSITION, ELEMENT AND PROCESS BACKGROUND OF THE INVENTION 2. Description of the State of the Art Photothermographic materials and methods of their preparation are known. Such photothermographic materials after imagewise exposure are overall heated to provide a developed image in the absence of separate processing solutions. Typical photothermographic materials are described, for example, in Belgian Pat. No. 765,452 issued May 28, 1971; Belgian Pat. No. 765,602 issued May 28, 1971; Belgian Pat. No. 765,601 issued May 28, 1971; Belgian Pat. No. 766,590 issued June 15, 1971; Belgian Pat. No. 766,589 issued June 15, 1971; Belgian Pat. No.

772,371 issued Oct. 15, 1971; US. Pat. 3,152,904 of Sorensen et al. issued Oct. 13, 1964; US. Pat. No. 3,457,075 of Morgan et al. issued July 22, 1969; US. Pat. 3,392,020 of Yutzy et al. issued July 9, 1968 and British Specification 1,161,777 published Aug. 20, 1969.

It has been desirable to provide increased photosensitivity to certain wavelengths of light in photothermographic materials. This is defined and employed herein as the sensitivity to ranges of electromagnetic radiation to which the photothermographic materials are exposed imagewise to provide a latent image. It has also been desirable in some cases to provide increased contrast of the images produced with the described photothermographic materials.

One means, which has been proposed to increase photosensitivity, centers upon preparation of photosensitive silver halide in the photothermographic materials. This method provides so-called silver halide in situ. This is described, for example, in US. Pat. No. 3,457,075 of Morgan et al. issued July 22, 1969. Preparation of the photosensitive silver halide in situ is difficult to control. Accordingly, it is desirable to provide the photosensitive silver halide separate from other components of the photothermographic composition and then mix the silver halide with the described components. This silver halide, prepared separate from other components of the photothermographic material, is referred to herein as ex situ silver halide. Photothermographic materials containing so-called ex situ silver halide are described, for example, in Belgian Pat. No. 774,436 issued Nov. 12, 1971. The described photothermographic materials contain silver halide which is prepared employing a polymeric peptizer. A typical polymeric peptizcr employed for this purpose is poly(- vinyl butyral). The silver halide can then be mixed with other components of the photothermographic composition such as an oxidation-reduction image-forming combination comprising (1) a silver salt oxidizing agent, such as silver behenate, and (2) an organic reducing agent, such as a sulfonamidophenol reducing agent.

Other means have been employed for providing increased sensitivity in photothermographic materials such as addition of onium halides as described in US. Pat. No. 3,679,422 ofv deMauriac and Hiller'. issued July 25, 1972. It was found, however, that mere addition of equivalent amounts of bromide ion or bromide compounds does not provide desired sensitivity. This is illustrated in following comparative Example 6. Also, mere addition of silver iodide to a photothermographic composition comprising an oxidation-reduction image-forming combination containing (1) a silver salt oxidizing agent, such as silver behenate, with (2) an organic reducing agent, such as a sulfonamidophenol reducing agent, with poly(vinyl acetal) peptized silver halide in a polymeric binder does not provide desired increased photosensitivity to the desired wavelength of light.

Iodide compounds have been'added to certain silver halide photosensitive materials as described in Photographic Science and Engineering, Vol. 14, No. 4, July-Aug., 1970, pages 258-261 and 262-268. Neither US. Pat. No. 3,679,422 nor theabove article suggests the photothermographic materials or preparation as described herein.

There has been a continuing need to provide a photothermographic element, composition and process for preparing the described photothermographic materials which provides increased photosensitivity to certain wavelengths of light without adversely affecting other desired sensitometric properties.

SUMMARY OF THE INVENTION dide or ammonium iodide, in a photothermographic composition and element comprising a dispersion of (a) an oxidation-reduction image-forming combination comprising (i) a silver salt oxidizing ,agent, and (ii) anorganic reducing agent, with (b) ex situ, synthetic polymer peptized photosensitive silver halide, (c) a cyclic imide toner, and (d) a polymeric binder whereinthe non-silver iodide salt has the property of increasing the desired photosensitivity of the photothermographic composition. The described non-silver iodide salt can be mixed with the described photothermographic compositions at different stages of preparation of the compositions depending on such factors as the wavelengths to be used for imagewise exposure and particular 10mporients of the photothermographic material. The surprising increase in photosensitivity to certain wavelengths of light is illustrated by comparative examples and the results set out in the following tables.

DETAILED DESCRIPTION OF THE INVENTION A range of non-silver iodide compounds can be employed according to the invention. The non-silver iodide salt, however, must have the property of increasing the photosensitivity of the described photothermographic materials to the desired wavelengths of light for imagewise exposure. Merely adding a silver iodide emulsion to the photothermographic materials does not provide the desired increase in photosensitivity. Accordingly, the term non-silver iodide compounds or salts as employed herein is intended to exclude silver iodide. One test which can be employed to determine a suitable non-silver iodide salt is set out in following Example 1. According to this test, if increased relative speed is provided to the desired wavelengths of light for imagewise exposure by the non-silver iodide salt tested, the iodide is considered to be acceptable. The useful concentration of non-silver iodide salt in this test is about 0.01 mole to about 0.50 moles of the described non-silver iodide salt per mole of the photosensitive silver halide in the photothermographic material. Acceptable non-silver iodide salts according to the invention are, for instance, lithium iodide, ammonium iodide, sodium iodide, potassium iodide and mixtures of these iodides. Choice of an optimum non-silver iodide salt and the optimum step in preparation of the photothermographic material for addition of the non-silver iodide salt will depend upon the particular photothermographic composition, desired image, processing conditions and the like. Lithium iodide is especially useful when employing a sulfonamidophenol reducing agent with a silver salt oxidizing agent, such as silver behenate, and an ex situ, poly(vinyl butyral) peptized photosensitive silver bromide in a polymeric binder such as poly(vinyl butyral).

A range of concentration of the described non-silver iodide salt can be employed. The concentration must be sufficient to provide the desired increase in photosensitivity in the described photothermographic composition. Typically, a concentration of non-silver iodide salt is about 0.01 mole to about 0.50 mole of the described non-silver iodide salt per mole of photosensitive silver halide in the described photothermographic material. A concentration of non-silver iodide salt which is about 0.01 mole to about 0.05 mole of the iodide, typically lithium iodide, per mole of the described silver halide is usually preferable.

The method of preparing the described photothermographic composition and element comprising a dispersion of oxidation-reduction image-forming combination with ex situ, synthetic polymer peptized photosensitive silver halide, and a cyclic imide toner in a polymeric binder can vary depending on the particular photothermographic material, desired image, processing conditions and the like. A typical method of preparing the dispersion involves thoroughly mixing the described components. These can be mixed employing any suitable apparatus such as a ball-mill or similar mixing means. One method of preparing the described dispersion and means for preparing the dispersion are set out, for instance, in Belgian Pat. No. 774,436 issued Nov. 12,1971.

The photothermographic elements and compositions according to the invention comprise an oxidationreduction image-forming combination which contains a silver salt oxidizing agent. The silver salt oxidizing agent can be a silver salt of an organic acid such as a fatty acid which is resistant to darkening upon illumination. An especially useful class of silver salts of organic acids is represented by the water insoluble silver salts of long-chain fatty acids which are stable to light. Compounds which are suitable silver salt oxidizing agents include, for instance, silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxy stearate, silver caprate, silver myristate and silver palmitate with silver stearate and silver behenate being especially useful. In some instances silver salts can be employed as the silver salt oxidizing agent which are not silver salts of longchain fatty acids. Such silver salt oxidizing agents which are useful include, for example, silver benzoate, silver benzotriazole, silver terephthalate, silver phthalate and the like. In most instances, however, silver behenate is most useful.

A variety of organic reducing agents can be employed in the described oxidation-reduction image forming combination. Sulfonamidophenol reducing agents are especially useful in the described oxidationreduction image-forming combination. Sulfonamidophenol reducing agents in photothermographic materials are described in US. Application Ser. No. 272,832 of Evans and McLaen, filed July 18, 1972. The sulfonamidophenol reducing agents useful according to the invention can be prepared employing known procedures in the art and include such compounds as described in Canadian Pat. No. 815,526 of Bard issued June 17, 1969. A useful class of sulfonamidophenol reducing agents according to the invention, is represented by the structure:

wherein R and R are each selected from the group consisting of hydrogen; chlorine; bromine; iodine; alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl and butyl; aryl containing 6 to 12 carbon atoms such as phenyl and tolyl; arylsulfonyl containing 6 to 12 carbon atoms, such as phenylsulfonyl; amino; hydroxy; alkoxy containing 1 to 4 carbon atoms, such as methoxy and ethoxy; and atoms completing with R and R a naphthalene nucleus;

Z and Z are each selected from the group consisting of hydrogen; bromine; chlorine; alkyl containing 1 to 4 carbon atoms, as described; aryl containing 6 to 10 carbon atoms, such as phenyl and tolyl; arylsulfonyl containing 6 to 12 carbon atoms, as described; amino; hydroxy; alkoxy containing 1 to 4 carbon atoms, such as methoxy and ethoxy; and R SO NH- wherein R is alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl and butyl; aryl containing 6 to 10 carbon atoms, such as phenyl and tolyl and hetero ring substituents, such as thienyl, quinolinyl and thiazyl,

o o o Z is hydrogen, alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl or butyl, chlorine and bromine when R and R are other than atoms completing containing l to 3 carbon atoms such as methyl, ethyl,

and propyl, chlorine, bromine and phenyl. In some cases it is desirable to avoid an amino group as a substituent. The amino group, in some cases, provides an overly active reducing agent.

One especially useful class of sulfonamidophenol reducing agents are compounds of the formula:

wherein R is phenyl, naphthyl, methylphenyl, thienyl, quinolinyl, thiazyl, or alkyl containing 1 to 4 carbon atoms,

as described;

R is hydrogen, R SO NH, alkoxy containing 1 to 4 carbon atoms, hydroxy, alkyl containing 1 to 4 carbon atoms, bromine or chlorine;

R is hydrogen, bromine, chlorine, alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl or butyl, or alkoxy containing 1 to 4 carbon atoms, such as methoxy, ethoxy and propoxy. R, R and/or R can contain substituent groups which do not adversely affect the reducing properties of the described sulfonamidophenol reducing agents or the desired sensitometric properties of the photothermographic elements and materials of the invention. These substituent groups are the same as described for generic structure I.

Another class of sulfonamidophenol reducing agents which are useful in photothermographic elements and compositions of the invention are sulfonamidonaphthols ofthe formula:

The sulfonamidophenol group in the described sulfonamidonaphthols can be in the ortho, meta or para position. The sulfonamidonaphthols are more active compounds within the sulfonamidophenol reducing agent class. Also, within this class, sulfonamidophenols which contain three sulfonamidophenol groups are more active. These sulfonamidophenols are employed for shorter developing times or with heavy metal salt oxidizing agents which are less active than silver behenate. In some cases, image discrimination provided by photothcrmographic materials containing the sulfonamidonaphthols and trifunctional sulfonamidophenols is less than that provided by other of the scribed sulfonamidophenols.

Combinations of sulfonamidophenol reducing agents, as described, can be employed in photothermographic materials and elements according to the inven tion. Especially useful sulfonamidophenol reducing agents include benzenesulfonamidophenol reducing agents, such as 2,6-dichloro-4- benzenesulfonamidophenol and/or 4- benzenesulfonamidophenol.

Other organic reducing agents which can be employed alone or in combination with the described sulfonamidophenol reducing agents include substituted phenols and naphthols, for example, bis-B-naphthols, such as described in US. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972. Suitable bis-B-naphthols include, for instance, 2,2'-dihydroxy-l,1-binaphthyl; 6,- 6-dibromo-2,2-dihydroxy-1,1-binaphthyl; 6,6- dinitro-2,2'-dihydroxy-l,1'-binaphthyl and/or bis-(2- hydroxy-l-naphthol) methane. Other reducing agents which can be employed in the described photothermographic materials according to the invention include polyhydroxybenzenes such as hydroquinone, alkylsubstituted hydroquinones such as tertiary butyl hydroquinone, methyl hydroquinone, 2,5-dimethyl hydroquinone and 2,6-dimethyl hydroquinone; catechols and pyrogallols; aminophenol reducing agents, such as 2,4- diaminophenols and methylaminophenols; ascorbic acid developing agents such as ascorbic acid and ascorbic acid derivatives such as ascorbic acid ketals; hydroxylamine developing agents; 3-pyrazolidone developing agents such as l-phenyl-3-pyrazolidone and the like. Combinations of these reducing agents can be em,- ployed if desired. The selection of an optimum reducing agent or reducing agent combination will depend upon particular photothermographic material, silver salt oxidizing agent, processing conditions,' desired image and the like.

A so-called activator-toning agent, also known as-an accelerator-toning agent or toner, can be employed in the photothermographic materials according to the in-' vention to obtain a desired image. The activator-toning agent is a cyclic imide and is typically useful in a range of concentration such as a concentration of about 0.10 mole to about 1.1 mole of activator-toning agent per mole of silver salt oxidizing agent in the photothermographic material. Typical suitable activator-toning agents are described in Belgian pat. No. 766,590 issued June 15, 1971. Typical activator-toning agents include, for example, 1 phthalimide, N-hydroxyphthalimide, N-hydroxy-l,8-naphthalimide, N-potassium phthalimide, N-mercury phthalimide, succinimide and/or N- hydroxysuccinimide. Combinations of so-called activator-toning agents can be employed if desired. Other activato r-toning agents which can be employed include phthalazinone, 2-acetyl-phthalazinone and the like.

A photothermographic element, as described according to the invention, can contain various non-gelatin compounds alone or in combination as vehicles, binding agents and in various layers. Suitable materials can be hydrophobic or hydrophilic. They are transparent or translucent and include such synthetic polymeric substances as water soluble polyvinyl compounds like poly(vinyl pyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds which can be employed include dispersed vinyl compounds such as in latex form and particularly those which increase dimensional stability of photographic materials. Effective polymers include water insoluble polymers of polyesters, polycarbonates, alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates, methacrylates and those which have crosslinking sites which facilitate hardening or curing as well as those having recurring sulfobetaine units as described in Canadian Pat. No. 774,054. Especially useful high molecular weight materials and resins include poly(vinyl butyral), cellulose acetate butyrate, polymethyl methacrylate, poly(vinyl pyrrolidone), ethylcellulose, polystyrene, polyvinyl chloride, chlorinated rubber, polyisobutylene, butadiene-styrene copolymers, vinyl chloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and maleic acid and polyvinyl alcohol.

The described non-silver iodide salt can be mixed with the described photothermographic compositions at different stages of preparation of the composition. The optimum stage of addition will depend on such factors as the wavelength to be used for imagewise exposure of the photothermographic composition, particular components of the photothermographic materials, desired image, particular activator-toning agent and the like.

Accordingly, one embodiment of the invention comprises a method of preparing a silver halide photothermographic composition or element comprising respectively A. preparing a dispersion of silver behenate in poly(- vinyl butyral),

B. mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition,

C. mixing with the resulting composition (i) an ex situ, poly(vinyl butyral) peptized photosensitive silver halide, and

D. a poly(vinyl butyral) binder, and

E. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting'composition.

Another embodiment of the invention comprises a method of preparing a silver halide, photothermographic composition or element comprising respec tively A. preparing poly( vinyl butyral) peptized photosensitive silver halide,

B. mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide,

C. mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), and

D. then mixing succinimide, a sulfonamidophenol re ducing agent and a spectral sensitizing dye with the resulting composition.

In preparing a photothermographic material according to the invention, it is often desirable to mix the described non-silver iodide salt with the photothermographic material and then hold the resulting composition for a period of time until the desired sensitivity is achieved, such as about 10 seconds to about 48 hours at room temperature, that is about C. to about 30C. before any subsequent steps. It appears that this holding step provides some interaction which is desired for the described increase in photosensitivity. The exact mechanism of reaction which takes place is not fully understood.

After the holding period, the photothermographic composition can be coated on a suitable support to provide a photothermographic element.

Accordingly, a further embodiment of the invention comprises preparing a photothermographic composition comprising (A) preparing a dispersion of (a) an oxidation-reduction image-forming combination comprising (i) a silver salt oxidizing agent, typically silver behenate, and (ii) a sulfonamidophenol reducing agent, with (b) ex situ, synthetic polymer peptized photosensitive silver halide, in (c) a poly(vinyl butyral).

binder, and, after preparing the dispersion, (B) mixing with the dispersion about 0.01 mole to about 0.5 mole, of the described iodide salt, typically lithium iodide, per mole of the silver halide, and then (C) holding the resulting composition for a period of time until the desired sensitivity is achieved, such as about 10 seconds to about 43 hours at about 20C. to about 30C. before any subsequent step.

After the holding step, a photothermographic ele-- It is desirable, in some cases, to employ an image stabilizer and/or image stabilizer precursor in the described photothermographic materials of the invention. Typical image stabilizers or stabilizer precursors are described, for example, in Belgian Pat. No. 768,071 issued July 30, 1971. Typical stabilizer precursors include, for example, azole thioethers and blocked azoline thione stabilizer precursors as described in this Belgian patent'and described in US. Pat. No. 3,700,457 of Youngquist, issued Oct. 24, 1972. i

The described photothermographic compositions and elements according to the invention can contain various addenda to aid the compositions and elements such as development modifiers that function as additional speed-increasing compounds, hardeners, antistatic layers, plasticizers and lubricants, coating aids, brighteners, spectral sensitizing dyes, absorbing and filter dyes, also as described in the Product Licensing Index, Volume 92, Dec., 1971, publication 9232, pages lO7l l0. 1

Spectral sensitizing dyes can be used in the described photothermographic materials of the invention to confer additional sensitivity to the elements and compositions of the invention. Useful sensitizing dyes are described, for example, in the Product Licensing Index, Volume 92, Dec., 1971, publication 9232, pages 107-1 10, paragraph XV and Belgian Pat. No. 772,371 issued Oct. 15, 1971. For example, when a photother' mographic material is to be exposed imagewise to a socalled red laser, a spectral sensitizing dye which provides a sensitivity to the red region of the spectrum is employed in the described photothermographic material according to the invention.

The photothermographic compositions and other compositions according to the invention can be coated on a suitable support by various coating procedures including dip coating, air knife coating, curtain coating or extrusion coating using hoppers such as described in US. Pat. No. 2,681,294 of Beguin issued June 15, 1954. If desired, two or more layers can be coated simultaneously such as described in US. Pat. No. 2,761,791 of Russell, issued Sept. 4, 1956 and British Pat. No. 837,095.

A range of concentration of various components of the photothermographic materials can be employed according to the invention. A useful concentration of reducing agent is typically about 0.25 mole to about 4 moles of reducing agent, such as sulfonamidophenol reducing agent, per mole of photosensitive silver halide in the photothermographic material. In relation to the silver salt oxidizing agent employed, a useful concentration range of reducing agent is typically about 0.10 mole to about 20.0 moles of reducing agent per mole of silver salt oxidizing agent, such as silver behenate and/or silver stearate. If a combination of reducing agents is employed, the total concentration of reducing agent is typically within the described concentration range.

It is believed that upon imagewise exposure the latent image silver of the described photosensitive silver halide acts as a catalyst for the described oxidation imageforming combination. A typical concentration range of photosensitive silver halide is about 0.01 mole to about 20 moles of photosensitive silver halide per mole of silver salt oxidizing agent, for instance, per mole of silver behenate and/or silver stearate. Preferred photosensitive silver halides are silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide of mixtures thereof. The photosensitive silver halide can be coarse or fine-grain, very fine-grain photosensitive silver halide being especially useful. The photosensitive silver halide can be chemically sensitized, can be protected against the production of fog and/or stabilized against the loss of sensitivity during keeping, as described in the Product Licensing Index reference mentioned previously.

The described ex situ, synthetic polymer peptized photosensitive silver halide can be prepared with a range of synthetic polymer peptizers. Useful synthetic polymer peptizers include, for example, those described in US. Pat. No. 3,713,833 of Lindholm et al., issued Jan. 30, 1973 and US. Pat. No. 3,706,565 of Ericson, issued Dec. 19, 1972, and vinyl pyridine polymers, e.g., polymers of 2-vinyl pyridine, 4-vinylpyridine and 2-methyl-5-vinylpyridine.

Poly(vinyl acetals), such as poly(vinyl butyral), are especially useful as peptizers in the described preparation of ex situ silver halide. The procedure can be carried out in a non-aqueous medium under controlled reaction conditions. For instance, an organic solvent, such as acetone or methylisobutyl ketone, can be employed with the peptizer,such as po1y(vinyl butyral). An example of a suitable preparation of photosensitive silver halide is as follows: Lithium bromide, silver trifluoroacetate and poly(vinyl butyral) are mixed in acetone under controlled conditions. The resulting, finegrain silver bromide can then be mixed with an oxidation-reduction image-forming combination, such as a sulfonamidophenol with silver behenate, to provide a photothermographic material.

The silver halide employed in the practice of the invention can he unwashed or washed to remove soluble salts. In the latter case, the soluble salts can be removed by chill-setting and decantation or an emulsion containing the silver halide can be coagulation washed.

Poly((vinyl acetal) peptized photosensitive silver halide is useful and is described, for example, in Belgian Pat. No. 774,436 issued Nov. 12, 1971. The photosensitive silver halide is prepared according to this method by mixing a source of silver ions with a source of halide ions in the presence of a poly(vinyl acetal) such as poly(vinyl butyral). This polymer peptized photosensitive silver halide is especially useful when the photothermographic material contains a polymeric binder which is the same as the polymer employed to peptize the silver halide. For example, the polymeric binder can be poly(vinyl butyral) which can also be employed to peptize the photosensitive silver halide.

An especially useful embodiment of the invention is in a photothermographic composition comprising the combination of (a) an oxidation-reduction imageforming combination comprising (i) silver behenate and/or silver stearate with (ii) a sulfonamidophenol reducing agent, as described, with (b) poly(vinyl butyral) peptized silver halide in (c) a poly(vinyl butyral) binder, the improvement comprising (d) about 0.01 mole to about 0.5 mole, such as about 0.01 mole to about 0.15 mole, of lithium iodide per mole of the silver halide. With this composition an especially useful activator-toning agent is succinimide.

After imagewise exposure of the described photothermographic element according to the invention, typically to visible light, the resulting latent image can be developed merely by uniformly overall heating the element to moderately elevated temperatures. This merely involves overall heating the described photothermographic element from about C. to about 250C. such as for about 0.5 second to about 60 seconds. By increasing or decreasing the length of time of heating, a

higher or lower temperature within the described range can be employed depending upon the desired image, particular photothermographic material and the like. A developed image is typically produced within several seconds, such as about 0.5 second to about 60 seconds. A processing temperature of about C. to about C. is especially useful.

While visible light can be employed to produce the latent image, other sources of electromagnetic radiation can be employed. For example, the described photothermographic elements of the invention are useful for high intensity imagewise exposure. A laser can be employed to produce an image in the described photothermographic material.

Any suitable means can be used for providing the desired processing temperature range. The heating means can be a simple hot plate, iron, roller or the like.

Processing is usually carried out under ambient conditions of pressure and humidity. Conditions outside normal atmospheric pressure and humidity can be employed if desired.

If desired, one or more components of the photothermographic element described can be in one or more layers of the element. For example, in certain cases it can be desirable to include certain percentages of the reducing agent, activator toner, image stabilizer and/or stabilizer precursor in a protective layer over the photothcrmographic element. This in some cases can reduce migration of certain addenda in the layers of the photothermographic element.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 This is a comparative example. A silver behenate dispersion is prepared by ballmilling the following components for 100 hours:

silver behenate 50.0 g poly(vinyl butyral) 15.0 g methylisobutyl ketone 500 ml A photothermographic composition is prepared by combining 100 ml of the above-described dispersion with the following addenda in the order indicated:

l2.0 ml

The composition is then held 4 hours at room temperature, i.e., about 20C.

The above composition is coated at 6.9 ml/ft on unsubbed poly(ethylene terephthalate) film support. The element is also overcoated with the following composition at 2.3 ml/ft. 1

Poly [4,4-( hexahydro-4,7-methanoindan-- 50 g ylidene)diphenylene carbonate] Dichloroethane 95 ml Acetone 4 Silicone surfactant (Silicone L-522 0.5 of Union Carbide Co., U.S.A.)

The dried element is exposed sensitometrically to light for lO'- seconds with a Mark VII exposing device marketed by Edgerton, Germeshausen and Grier, Inc. and then overall heated for 5 seconds at l32C. The sensitometric results are given in Table 1.

EXAMPLE 2 This example is like Example 1 except that 4 ml of an acetone solution containing 2.28% by weight anhydrous lithium iodide is added to the described composition prior to coating. The element is sensitometrically exposed and processed by overall heating the exposed element for 5 seconds at 132C. as described in Example l. The sensitometric results appear in Table I.

Table I Relative Example Speed Contrast Dmin Dmax Table I-Continued *Relative Example Speed Contrast Dmin Dmax Measured at 0.30 above Dmin Density results are measured using a so-called Status A blue filter combination consisting of three Wratten 47B filters, one X12740 filter and one C9782 filter. This filter combination exhibits peak transmittance in the 440 nm region.

EXAMPLE 3 Results similar to those achieved in Example 2 are observed when potassium iodide is employed in place of lithium iodide.

EXAMPLE 4 Results similar to those achieved in Example 2 are observed when ammonium iodide is employed in place of lithium iodide.

EXAMPLE 4a Results similar to those achieved in Example 2 are observed when sodium iodide is employed in place of lithium iodide.

EXAMPLE 5 Results similar to those achieved in Example 2 are observed when sensitizing dye anhydro-9-ethyl-3,3- di(3-sulfopropyl)-4,5;4,5-dibenzothiacarbocyanine hydroxide, sodium salt is employed in place of the sensitizing dye described in Example 2. The lithium iodide salt promotes J-aggregation of the dye at 680-690 nm.

EXAMPLE 6 This is 'a comparative example.

No significant increase in photosensitivity is observed when the procedure described in Example 2 is repeated with the exception that sodium bromide is employed in place of lithium iodide. Sodium bromide accordingly does not have the property of increasing the photosensitivity of the described photothermographic materials under these conditions.

EXAMPLE 7 The procedure described in Example 2 is repeated with the exception that 0.05 mole of lithium iodide is employed per mole of the described photosensitive silver bromide in the photothermographic composition. Results similar to those of Example 2 are observed.

EXAMPLE 8 The procedure described in Example 2 is repeated with the exception that 0.25 mole of lithium iodide is employed per mole of the described photosensitive silver bromide in the photothermographic composition. Results similar to those of Example 2 are observed.

EXAMPLES 9-12 The photothermographic compositions employed in the photothermographic elements in Examples 9l2 are identical to those described in Example 2 except that the method of preparing the composition is changed. The accompanying Table II shows the order of addition of the components and the speeds observed. These examples indicate that by starting with either the silver behenate dispersion or the poly(vinyl buty- 14 by combining the following components in the order indicated:

1. silver behenate-behenic acid dispersion ral) peptized emulsion and then adding either the lithidfi t rl r ium iodide or suecinimide solutions before all the other 3- ilhium iodide components, even greater photosensitivity can be obpolyvinyl butyral-silver bromide emulsion tained. 5. additional poly(vinyl butyral) Table ll l AgBr AgBe Lil Toner PVB** Developer Phe- Surfactant Dye Speed* none*** Example Emul. Disp. Soln. Soln. Soln. Soln. Compound Soln. Soln. Ergs/cm (control) 9 1 4 3 2 5 6 7 8 9 805 10 1 4 2 3 5 6 7 8 9 885 11 4 1 3 2 5 6 7 8 9 855 12 4 l 2 3 5 6 7 8 9 1025 '2 X 10' seconds McCowan red laser exposure; a lower figure indicates a more sensitive element "PVB means poly(vinyl butyrall 2.4-dihydroxyhenznphenone EXAMPLES 13-20 The photothermographic compositions employed in these elements are identical to those described in Example 2 except that the method of preparing the final composition is changed. The order of addition for each component is indicated by a code in the far right hand column of the following Table 111. The code is ex plained at the bottom of Table lll. The results of Examples 13-20 are given in following Table 111.

In summary, the element most sensitive to red light, i.e., light to which the elements have been spectrally sensitized, is Example 15. This element was prepared Table Ill SPECTRALLY SENSITIZED COATINGS Clear lue Red Order Rel. Rel. Rel. of Ex. Speed* 7 Dmin Dmax Speed* 7 Dmin Dmax Speed* 7 Dmin Addition max 13 0.91 0.20 1.45 100 0.66 0.18 0.62 100 0.84 0.18 0.80 DTEOADy 14 166 1.07 0.18 1.78 550 1.14 0.20 1.43 102 1.14 0.20 1.24 DTEOADyl 15 148 1.01 0.20 1.88 282 1.19 0.18 1.21 204 1 21 0.18 1.54 DTlEOADy 16 141 1.33 0.17 2.00 457 1.11 0.20 1.41 186 1 11 0.20 1 35 ETIDOADy 17 162 1.11 0.18 1.84 468 1.15 0.22 1.44 1.06 0.21 1 32 l-IlTDOADy NON-SPECTRALLY SENSlTlZED COATlNGS 18 100 0.65 0.17 1.16 100 0.62 0.20 0.96 DTEOAI 19 74 1.21 0.16 1.77 73 1.37 0.17 1.29 DTIEOA 20 87 0.70 0.18 1.37 91 0.75 0.20 1.02 ETIDOA Exposure: 10 E0 and G Process: 5"/130C Blue exposure: Wrattcn 47B filter Red exposure: Dichroic Wrattcn 29 filter combination; 642nm peak transmission *Rclative speed is measured at 0.30 above Dmin The following is a key to the order of addition of the designated components in preparation of the described photothermographic materials:

0A: Other addenda, e.g. polyvinylbutyral, developer, 2,4-dihydroxyhcnzophenone,

respectively D: Silver behenate, polyvinylbutyral, methylisobutyl kctone dispersion T: Succinimidc toner l: Lithium iodide/acetone solution E; Polyvinylbutyral-silver bromide-acetone emulsion Dy: Spectral sensitizing dye EXAMPLES 21-28 The photothermographic compositions employed in these elements are the same as described in Example 2. The order of addition for each component is indicated by the code following Table IV. The results are given .in following Table IV.

Table IV CLEAR EXPOSURE RED EXPOSURE Rel. Rel. Order of*** Example Speed* y Dmin Dmax Speed* y Dmin Dmax Addition 21 100 0.21 0.10 0.41 100 0.18 0.10 .40 DEOADy (comparative example) 22 447 0.38 0.12 0.81 118 0.30 0.12 0.44 DlEOADy 23 676 0.36 0.13 0.68 85 0.26 0.13 0.40 DElOADy 24 1000 0.31 0.15 0.62 138 0.17 0.15 0.48 ElDOADy 25 4470 1.55 0.44 2.26 1410 1.30 0.41 2.10 DTpEOADy (comparative example) 26 3550 1.83 0.27 2.28 1380 1.40 0.24 1.79 DTplEOADy 27 5500 2.03 .38 2.34 955 1.66 0.42 2.07 DTpEOADyl 28 5130 1.46 .39 2.16 1450 1.21 0.41 1.82 ETplDOADy Exposure: 10" E and G Process: "/150"C Clear Exposure: non-filter light Red Exposure: Dichroic Wratten 29 *Relative speed measured at 0.30 above Dmin filter combination; 642 nm peak transmission The following is a key to the order of addition of the designated components in preparation of the described photothermographic materials:

O Other addenda; e.g. polyvinylbutyral. developer, 2,4-dihydroxybcnzophenone.

silicone AF-70, respectively D: Silver behenate, polyvinylbutyral dispersion Tp: Phthalazinone toner l: Lithium iodide E: Washed polyvinylbutyral-silvcr bromide emulsion Dy: Spectral sensitizing dye b. a synthetic polymer-peptized photosensitive sil-' ver halide, and

c. a cyclic imide toner in d. a non-gelatin polymeric binder, the improvement comprising:

B. mixing with said dispersion a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition.

2. A method as in claim 1 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of' said iodide salt per mole of said photosensitive silver halide.

3. A method as in claim 1 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide and ammonium iodide and combinations of these iodide compounds.

4. A method as in claim 1 wherein said toner comprises succinimide.

5. A method as in claim 1 of preparing a photothermographic composition also comprising, after said mixing, holding the resulting composition for about seconds to about 48 hours at about C. to about 30C. before any subsequent step.

b. a cyclic imide toner comprising succinimide, c. a poly(vinyl butyral) peptized silver halide in d. a poly(vinyl butyral) binder, and, after preparing said dispersion:

B. mixing with said dispersion about 0.01 mole to about 0.50 mole of lithium iodide per mole of said silver halide.

7. A method of preparing a photothermographic composition comprising:

A. preparing a dispersion of:

a. an oxidation-reduction image-forming combination comprising:

i. silverbehenate and ii. 4-benzenesulfonamidophenol and 2,4-dihydroxybenzophenone, and b. a cyclic imide toner comprising succinimide, c. poly(vinyl butyral) peptized silver bromide in d. a poly(vinyl butyral) binder, and, after preparing said dispersion, B. mixing with said dispersion about 0.01 mole to about 0.05, mole of lithium iodide per mole of said silver bromide, and then C. holding the resulting photothermographic composition for about minutes to about 4 hours at about 20C. to about 30C. before any subsequent step. 8. A method of preparing a silver halide photothermographic composition comprising respectively A. preparing a dispersion of silver behenate in poly(- vinyl butyral), B. mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition, C. mixing with the resulting composition an ex situ, poly(vinyl butyral) peptized photosensitive silver halide, and

D. a poly(vinyl butyral) binder, and E. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.

9. A method of preparing a silver halide photothermographic composition comprising respectively A. preparing poly( vinyl butyral) peptized photosensitive silver halide, B. mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide,

C. mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), and

D. then mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.

10. In a method of preparing a photothermographic element comprising:

A. preparing a dispersion of:

a. an oxidation-reduction image-forming combination comprising: i. a silver salt oxidizing agent and ii. an organic reducing agent with:

b. synthetic polymer-peptized photosensitive silver halide, and

c. a cyclic imide toner in d. a non-gelatin polymeric binder, the improvement comprising, after preparing said dispersion B. mixing with said dispersion a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition,

C. holding the resulting composition for about seconds to about 48 hours at about 20C. to about 30c. and then D. coating the photothermographic composition on a support.

11. A method as in claim 10 of preparing a photothermographic element wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.

12. A method as in claim 10 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.

13. A method of preparing a photothermographic element comprising:

A. preparing a dispersion of:

a. an oxidation-reduction image-forming combination comprising: i. silver behenate and ii. 4-benzenesulfonamidophenol and 2,4-dihydroxybenzophenone, and

b. poly(vinyl butyral) peptized silver halide in c. a poly(vinyl butyral) binder, and, after preparing said dispersion:

B. mixing with said dispersion about 0.15 mole to about 0.30 mole of lithium iodide per mole of said silver bromide, then C. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20 C. to about 30 C., and then D. coating the photothermographic composition on a support.

14. A method of preparing a photothermographic element comprising respectively A. preparing a dispersion of silver behenate in poly(- vinyl butyral),

B. mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition,

C. mixing with the resulting composition a poly(vinyl butyral) peptized photosensitive silver halide, and

D. a poly(vinyl butyral) binder,

E. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition, then F. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20C.to about 30C., and then G. coating the photothermographic composition on a support.

15. A method of preparing a photothermographic element comprising respectively A. preparing poly(vinyl butyral) peptized photosensitive silver halide,

B. mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide,

C. mixing with the resulting composition a disperrion of silver behenate in poly(vinyl butyral),

D.mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with resulting composition,

E. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20C. to about 30C. and then F. coating the photothermographic composition on a support.

16. In a photothermographic composition comprising the combination of:

a. an oxidation-reduction image-forming combination comprising:

i. a silver salt oxidizing agent with ii. an organic reducing agent,

b. a synthetic polymer-peptized photosensitive silver halide, and

c. a cyclic imide toner in a polymeric binder, the

improvement comprising:

(1. a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition.

17. A photothermographic composition as in claim 16 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.

18. A photothermographic composition as in claim 16 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.

19. A photothermographic composition as in claim 16 wherein said toner comprises succinimide.

20. In a photothermographic composition comprising the combination of:

a. an oxidation-reduction image-forming combination comprising:

i. silver behenate with ii. a sulfonamidophenol reducing agent with b. poly(vinyl butyral) peptized silver halide,

c. succinimide, and

d. a poly(vinyl butyral) binder for said composition, the improvement comprising:

e. about 0.01 mole to about 0.05 mole of lithium iodide per mole of said silver halide.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,871,887

DATED March 18, 1975 |NVENTOR(5) 3 Cynthia G. Jones It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown betow:

Column 9, line 33, "of should read --OI--.

Column 10, line t, "Poly((v1nyl acetal)" should read --Poly(vinyl acetal)-.

Column l7, line 36, "30C." should read ---30C..

Signed and Sealed this fourteenth Day Of October 1975 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN A IPSIing Offic Commissioner of Parents and Trademarks 

1. IN A METHOD OF PREPARING A PHOTOTHERMOGRAPHIC COMPOSITION COMPRISING: A. PREPARING A DISPERSION OF: A. AN OXIDATION-REDUCTION IMAGE-FORMING COMBINATION COMPRISING: I. A SILVER SALT OXIDIZING AGENT AND II. AN ORGANIC REDUCING AGENT WITH: B. A SYNTHETIC POLYMER-PEPTIZED PHOTOSENSITIVE SILVER HALIDE, AND C. A CYCLIC IMIDE TONER IN D. A NON-GELATIN POLYMERIC BINDER, THE IMPROVEMENT COMPRISING: B. MIXING WITH SAID DISPERSION A SENSITIZING CONCENTRATION OF A NON-SILVER IODIDE SALT, SAID IODIDE SALT HAVING THE PROPERTY OF INCREASING THE PHOTOSENSITIVITY OF SAID PHOTOTHERMOGRAPHIC COMPOSITION.
 2. A method as in claim 1 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.
 3. A method as in claim 1 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide and ammonium iodide and combinations of these iodide compounds.
 4. A method as in claim 1 wherein said toner comprises succinimide.
 5. A method as in claim 1 of preparing a photothermographic composition also comprising, after said mixing, holding the resulting composition for about 10 seconds to about 48 hours at about 20*C. to about 30*C. before any subsequent step.
 6. A method of preparing a photothermographic composition comprising A. preparing a dispersion of: a. an oxidation-reduction image-forming combination comprising i. silver behenate and ii. a sulfonamidophenol reducing agent with: b. a cyclic imide toner comprising succinimide, c. a poly(vinyl butyral) peptized silver halide in d. a poly(vinyl butyral) binder, and, after preparing said dispersion: B. mixing with said dispersion about 0.01 mole to about 0.50 mole of lithium iodide per mole of said silver halide.
 7. A method of preparing a photothermographic composition comprising: A. preparing a dispersion of: a. an oxidation-reduction image-forming combination comprising: i. silver behenate and ii. 4-benzenesulfonamidophenol and 2,4-dihydroxybenzophenone, and b. a cyclic imide toner comprising succinimide, c. poly(vinyl butyral) peptized silver bromide in d. a poly(vinyl butyral) binder, and, after preparing said dispersion, B. mixing with said dispersion about 0.01 mole to about 0.05 mole of lithium iodide per mole of said silver bromide, and then C. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20*C. to about 30*C. before any subsequent step.
 8. A method of preparing a silver halide photothermographic composition comprising respectively A. preparing a dispersion of silver behenate in poly(vinyl butyral), B. mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition, C. mixing with the resulting composition an ex situ, poly(vinyl butyral) peptized photosensitive silver halide, and D. a poly(vinyl butyral) binder, and E. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.
 9. A method of preparing a silver halide photothermographic composition comprising respectively A. preparing poly(vinyl butyral) peptized photosensitive silver halide, B. mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide, C. mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), and D. then mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.
 10. In a method of preparing a photothermographic element comprising: A. preparing a dispersion of: a. an oxidation-reduction image-forming combination comprising: i. a silver salt oxidizing agent and ii. an organic reducing agent with: b. synthetic polymer-peptized photosensitive silver halide, and c. a cyclic imide toner in d. a non-gelatin polymeric binder, the improvement comprising, after preparing said dispersion B. mixing with said dispersion a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition, C. holding the resulting composition for about 10 seconds to about 48 hours at about 20*C. to about 30*c. and then D. coating the photothermographic composition on a support.
 11. A method as in claim 10 of preparing a photothermographic element wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.
 12. A method as in claim 10 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.
 13. A method of preparing a photothermographic element comprising: A. preparing a dispersion of: a. an oxidation-reduction image-forming combination comprising: i. silver behenate and ii. 4-benzenesulfonamidophenol and 2,4-dihydroxybenzophenone, and b. poly(vinyl butyral) peptized silver halide in c. a poly(vinyl butyral) binder, and, after preparing said dispersion: B. mixing with said dispersion about 0.15 mole to about 0.30 mole of lithium iodide per mole of said silver bromide, then C. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20* C. to about 30* C., and then D. coating the photothermographic composition on a support.
 14. A method of preparing a photothermographic element comprising respectively A. preparing a dispersion of silver behenate in poly(vinyl butyral), B. mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition, C. mixing with the resulting composition a poly(vinyl butyral) peptized photosensitive silver halide, and D. a poly(vinyl butyral) binder, E. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition, then F. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20*C. to about 30*C., and then G. coating the photothermographic composition on a support.
 15. A method of preparing a photothermographic element comprising respectively A. preparing poly(vinyl butyral) peptized photosensitive silver halide, B. mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide, C. mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), D. mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with resulting composition, E. holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20*C. to about 30*C. and then F. coating the photothermographic composition on a support.
 16. In a photothermographic composition comprising the combination of: a. an oxidation-reduction image-forming combination comprising: i. a silver salt oxidizing agent with ii. an organic reducing agent, b. a synthetic polymer-peptized photosensitive silver halide, and c. a cyclic imide toner in a polymeric binder, the improvement comprising: d. a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition.
 17. A photothermographic composition as in claim 16 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.
 18. A photothermographic composition as in claim 16 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.
 19. A photothermographic composition as in claim 16 wherein said toner comprises succinimide.
 20. In a photothermographic composition comprising the combinAtion of: a. an oxidation-reduction image-forming combination comprising: i. silver behenate with ii. a sulfonamidophenol reducing agent with b. poly(vinyl butyral) peptized silver halide, c. succinimide, and d. a poly(vinyl butyral) binder for said composition, the improvement comprising: e. about 0.01 mole to about 0.05 mole of lithium iodide per mole of said silver halide. 